Was it the best third version game?
>adds animated sprites
>better spritework in general
>revamped tilesets for the overworld
>slick black UI
>introduces recurring character Looker
>adds more alt forms before the gimmick overstayed it's welcome
>you can have your own villa
>return of the battle frontier with some different facilities
>fun wi-fi plaza
>Cyrus plotline improved thanks to input for Nob Ogasawara
>expanded regional dex
>raised difficulty for certain battles
>improves protagonist designs
>fixes some slowness for the base games like surf speed
>other minor improvements like pokeradar grass patches being more clearly visible

Yes D/P were not the best debut games to begin with, but Pt enhance them enough to make them great. The same cannot be said for USUM, because while it does add a bunch of new stuff, not much of it actually improves on the experience, and in some cases it is worse like storyline. They also didn't bother redecorating the region outside of route one and the first city.